In 2009 the International Energy Conservation Code mandated programmable thermostats be installed in new construction. Additionally many of the homes built prior to that have been upgraded with programmable thermostats to improve the energy efficiency of their homes.
The problem with a programmable thermostat is that almost all of the systems rely on a battery powered microprocessor to control zone temperature. When the battery fails or the programming becomes corrupt there is no signal to the furnace/boiler or the air conditioning unit.